For the first 1,000 rounds, buy factory. For reloading it would be
$5.00 Reloading tools
$2.40 1,000 primers
$3.60 for 6 lbs of gunpowder at the trading post price of 60 cents per pound (40 grains per cartridge)
$4.35 for 29 lbs of lead at the trading post price of 15 cents per pound (200 grain bullets)
$15.35 for 2nd 1,000 rounds and $10.35 for the 3rd 1,000 rounds. Add a $1.65 for buying bullets, instead of casting.
If you bought at a rail head, like Dodge City, gunpowder would cost 44 cents per pound and lead 13 cents per pound.
$13.81 for 2nd 1,000 rounds and $8.81 for the 3rd 1,000 rounds.
I got the prices for gunpowder and lead in 1875 from "Adobe Walls: The History and Archaeology of the 1874 Trading Post"
By T. Lindsay Baker, Billy R. Harrison, B. Byron Price. It can be previewed on Google books. The prices were on page 26.